The process of finishing a surface of a workpiece, such as for example a propeller blade, high pressure compressor turbine blade, and the like requires precision techniques to determine the desired contour of the surface of the workpiece. Such workpieces typically include synthetic or free form curves.
In the case of refurbishing used compressor or high-pressure turbine blades or vanes, used blades are typically already distorted and/or deformed through use due to wear and tear. Additionally, if the tip or leading or trailing edge of the turbine blade is worn or damaged, the worn or damaged portion is removed or cut out of the blade edge. Exotic material is welded on to the blade edge in place of the removed worn or damaged area. The surface of the welded area requires finishing to make the welded surface flush with the turbine blade surface. Finishing the surface, in particular the tips of the blade, is traditionally carried out by hand. Of course, the consistency of the quality of the hand finishing depends entirely on the degree of skill of the manual operator.
Attempts have been made to replace the manual operator with an automated system. However, as each used turbine blade develops a unique profile through use, which is different from the original profile of a new unused turbine blade as manufactured, methods are required to predict and generate the profiles of each used blade surface.
For example, U.S. Pat. No. 6,100,893, issued on 8 Aug. 2000 to Ensz et al., describes a process to reconstruct the profile of a workpiece by use of a computer for constructing geometric models of shapes. The representations of surfaces and solids corresponding to a collection of data points are produced by use of implicit functions based on a set of layer surface points of the object workpiece. The process of U.S. Pat. No. 6,100,893 however is unable to perform the profile reconstruction of on object where the original layer of the object cannot be measured, which is required in many applications such as for example refurbishment of turbine blades.
U.S. Pat. No. 4,686,796, issued on 18 Aug. 1987 to Giebmanns, describes a process and apparatus for polishing turbine blades to provide a circle segment approach to form complex curves. However, it does not include a practical implementation of a profile or reconstruction machining process.
Therefore, there is a need for a method of determining a surface of a workpiece to reconstruct the profile of a surface of a workpiece having synthetic or free form curves, such as for example the surface of a used turbine blade. Another need exists for a method to reconstruct the profile of a surface of a workpiece such as a used turbine blade even if the surface of the used workpiece is distorted and/or deformed with reference to an unused workpiece. There is another need for a method of determining a surface of a workpiece such that the profile of the workpiece that is generated may be used in the performance of the finishing processes by equipment such as a computer numerical control (CNC) machine, a robotic polishing/grinding system or the like. At the same time the method needs to achieve results that meet the strict requirements and maximum acceptable fault tolerance, whilst predicting the surface of a workpiece, for example a used turbine blade that may have been subjected to distortion and/or deformation.